On-chip resistor calibration in semiconductor devices

ABSTRACT

According to one disclosed embodiment, an on-chip resistor calibration circuit includes an RC oscillator having a test resistor and a precision capacitor as elements, a counter, and a reference clock. In one embodiment, an RC oscillator generates a waveform having a period dependent upon the resistance of the test resistor and the capacitance of the precision capacitor. In such an embodiment, a counter and a reference clock may be configured to measure the period of the waveform. Using a pre-determined capacitance of the precision capacitor, a resistance of the test resistor may be determined. In another embodiment, an RC oscillator generates first and second waveforms through use of an additional capacitor that can be switched in and out of the RC oscillator circuit. Using a pre-determined capacitance of the precision capacitor, an RC product of the test resistor and the additional capacitor may be determined.

This is a continuation of application Ser. No. 12/927,240, filed Nov.10, 2010 (now U.S. Pat. No. 8,476,911).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally in the field of semiconductors. Moreparticularly, the present invention is in the field of circuit elementcalibration.

2. Background Art

The proliferation of wireless communication devices has led tosignificant technological advances in the analog circuitry used intransceivers, converters, phase-locked loops and variable gainamplifiers, for example. Many of the advances have involved reducing thesize, complexity and cost of each device, as well as reducing theirpower consumption. However, as the field has become more populated,precision in the manufacturing and operation of these devices has becomeincreasingly important. For example, a cell phone transceiver must becapable of transmitting and receiving on precise channels within anavailable frequency band. In order to select specific channels, the cellphone must be able to precisely tune its transceiver so as to minimizecross talk with other transmissions.

In order to meet the requirements of low cost, low complexity and smallsize, many semiconductor manufactures choose to leverage conventionaland relatively inexpensive fabrication technology, such as that used toform polysilicon resistors (polyresistors) in semiconductor devices, forexample. But, as is known in the art, the actual resistance of aconventionally formed resistor can vary significantly from its desiredresistance, from wafer to wafer and from process-run to process-run,increasingly as the size of a resistor is scaled down. Moreover, theactual resistance of a conventionally formed resistor can varysignificantly with temperature. Fortunately, conventional resistors thatare formed together on a single wafer often exhibit the same type ofvariance from their desired resistance. So, by measuring the resistanceof one exemplary resistor on a single chip or die, one can calibrate allsimilarly fabricated resistors across a single-die semiconductor device,thereby providing the precision required by modern semiconductordevices.

Conventional calibration methods, which often require connections tooff-chip devices, are typically expensive, complex, and time-consumingto implement. For example, one conventional method uses a relativelyslow iterative process to match the resistance of an on-chip variableresistor block to that of an off-chip reference resistor. The externalreference resistor can be relatively expensive to fabricate, and thereis additional expense both in providing a precision via or pin on thesemiconductor device for a precision analog electrical connection, aswell as in providing sufficient mounting space and electrical noiseshielding for the reference resistor.

Thus, there is a need to overcome the drawbacks and deficiencies in theart by providing a simplified, inexpensive, and more time-efficientsystem for calibrating resistors in semiconductor devices.

SUMMARY OF THE INVENTION

A system and method for on-chip resistor calibration in semiconductordevices, substantially as shown in and/or described in connection withat least one of the figures, as set forth more completely in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an equivalent circuit schematic of a conventionaltechnique for calibrating resistors.

FIG. 2 illustrates a circuit schematic of an embodiment of the presentinvention.

FIG. 3 illustrates a circuit schematic of another embodiment of thepresent invention.

FIG. 4 shows a flowchart illustrating steps taken to implement a methodfor on-chip calibration of a circuit element, according to an embodimentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a system and method for on-chipresistor calibration in semiconductor devices. The following descriptioncontains specific information pertaining to the implementation of thepresent invention. One skilled in the art will recognize that thepresent invention may be implemented in a manner different from thatspecifically discussed in the present application. Moreover, some of thespecific details of the invention are not discussed in order not toobscure the invention.

The drawings in the present application and their accompanying detaileddescription are directed to merely exemplary embodiments of theinvention. To maintain brevity, other embodiments of the presentinvention are not specifically described in the present application andare not specifically illustrated by the present drawings. It should beunderstood that unless noted otherwise, like or corresponding elementsamong the figures may be indicated by like or corresponding referencenumerals. Moreover, the drawings and illustrations in the presentapplication are generally not to scale, and are not intended tocorrespond to actual relative dimensions.

FIG. 1 illustrates a conventional and relatively inefficient techniquefor calibrating resistors formed in a typical single-die transceiver.Conventional calibration system 100, in FIG. 1, is configured tocalibrate variable resistor 110 by matching the resistance of variableresistor 110 to the known resistance of external reference resistor 111.As shown in FIG. 1, current sources 120 and 121 provide substantiallythe same current to variable resistor 110 and external referenceresistor 111. The difference in voltages across the resistors (e.g., theoffset voltage) is amplified and/or buffered, as desired, bydifferential amplifier 130 and then provided to analog-to-digitalconverter (ADC) 140. ADC 140 converts the offset voltage and delivers itto the digital portion of the transceiver (e.g., the Digital Baseband)over bus 141. Using the offset voltage as a guide, a control signal isprovided over control lines 142 to variable resistor 110 to adjust itsresistance and incrementally reduce the offset voltage, as fed backthrough differential amplifier 130 and ADC 140. By performing multipleiterations of the above steps, the offset voltage can be minimized andthe resistance of variable resistor 110 can be made to substantiallymatch the known resistance of external reference resistor 111. Using thecontrol signal for a minimum offset voltage and the known resistance ofexternal reference resistor 111, the resistance of variable resistor 110may be derived, and all similarly fabricated resistors on thesemiconductor die can be calibrated accordingly.

As can be seen from the above explanation, as well as from FIG. 1, thisconventional technique requires the expense of forming external pin 112and making a precision analog electrical connection to externalreference resistor 111. Additionally, this conventional technique usesan iterative approach to match variable resistor 110 to externalreference resistor 111, which takes a relatively lengthy period of timeand, moreover, undesirably drains power resources during that time.

FIG. 2 illustrates an embodiment of the present invention that obviatesthe inefficiencies inherent in using a conventional calibrationtechnique such as the one depicted in FIG. 1. Calibration system 200, inFIG. 2, is configured to determine the resistance of test resistor 210by measuring the period of waveform 231 generated by test resistor 210in combination with other elements of a resistor-capacitor (RC)oscillator. Calibration system 200 may be formed on a portion of asemiconductor die as part of a single-die semiconductor transceiver, forexample, and may comprise test resistor 210, precision capacitor 220, RCoscillator 230 including test resistor 210 and precision capacitor 220,and counter 240. As can be seen from FIG. 2, all analog portions ofcalibration system 200 may reside on-chip, thereby eliminating the needfor a precision external analog connection. Furthermore, while referenceclock 250 may be provided by a device residing off-chip, reference clock250 may also be provided by a digital portion of the die (i.e., theDigital Baseband) so that no additional external connections arerequired.

Test resistor 210 may be an exemplary resistor or resistor networkconfigured to facilitate calibration of similarly fabricated resistorson the same die. For example, test resistor 210 may have a desiredresistance configured to be within a particular range of other resistorson the same die in order to simulate structural similarity, or may beconfigured to produce a waveform with a relatively long period in orderto provide a higher precision calibration, as is explained more fullybelow. Test resistor 210 may comprise one or more polyresistors, forexample, or may be any other type of resistor that can be fabricated ona semiconductor wafer or die.

Precision capacitor 220 may be any capacitor or capacitor networkconfigured to have a pre-determined capacitance that varies very littlefrom wafer to wafer, process-run to process-run, and over a widetemperature range. Additionally, precision capacitor 220 may beconfigured to have a pre-determined capacitance that varies very littlewith applied voltage. For example, precision capacitor 220 may compriseone or more metal-insulator-semiconductor (MIS) capacitors, such asmetal-oxide-semiconductor (MOS) capacitors, as known in the art, and maybe configured as one or more MIS varactors, as is also known in the art.An exemplary MOS varactor, for example, may exhibit a variation in itsactual capacitance over different wafers, process-runs, temperatures andapplied voltages that is less than 3% of its pre-determined capacitance.

RC oscillator 230 may be any oscillator circuitry that can be formed ona semiconductor wafer, for example, such that it can generate waveform231 having a period that corresponds to, e.g., is substantiallydependent upon, the resistance and capacitance of test resistor 210 andprecision capacitor 220. For example, waveform 231 may have a periodthat is substantially proportional to a product of the resistance oftest resistor 210 and the capacitance of precision capacitor 220.Although RC oscillator 230 is represented as having a specificconfiguration, that particular arrangement is not meant to limit thepresent inventive concepts. For example, although not explicitly shownin FIG. 2, RC oscillator 230 may be connected to a network of capacitorscomprising precision capacitor 220 and to a resistor network comprisingtest resistor 210 such that either or both test resistor 210 orprecision capacitor 220 are directly connected to ground. Moreover, andparticularly if test resistor 210 and/or precision capacitor 220 arenetworks of resistors and capacitors, respectively, RC oscillator 230may be configured to facilitate a particular RC oscillator topology,such as a topology producing a square-wave waveform, for example, or atopology producing a waveform with a relatively long period.

Counter 240 may be any circuitry that can be formed on a semiconductorwafer and be configured to measure a period of waveform 231 usingreference clock 250. Reference clock 250 may be a signal generated froma conventional crystal oscillator (XO) or a temperature compensatedcrystal oscillator (TOXO), for example, or any other reference clockgenerator known in the art. As explained above, reference clock 250 maybe provided by a digital portion of the same die on which RC oscillator230 is implemented, such that no additional external connection isrequired. Additionally, reference clock 250 may be configured to have afrequency that is significantly higher than that of waveform 231 inorder to facilitate accurate measurement of a period of waveform 231, asis explained more fully below.

As is known in the art, counter 240 may be configured to accept aninitialization signal over control lines 242 which resets its count andplaces it in a waiting mode until it senses a signal edge or zerocrossing, for example, of waveform 231. Upon sensing a signal edge orzero crossing, for example, counter 240 may then count the number ofcycles of reference clock 250 until it senses some number of latersignal edges or zero crossings of waveform 231. Once counter 240 hascompleted a count, counter 240 may deliver the count to the digitalportion of the die (e.g., the Digital Baseband) over bus 241. As will beexplained more fully below, the count may be used to determine theresistance of test resistor 210, thereby calibrating that type ofresistor across the entire semiconductor die. Thus, the presentinvention is capable of calibrating resistors on a semiconductor diewithout the expense of an external connection and without the time andpower needed for a conventional iterative technique.

Turning to FIG. 3, FIG. 3 illustrates an embodiment of the presentinvention that may be used for on-chip calibration of additional circuitelements fabricated on a semiconductor die. FIG. 3 shows calibrationsystem 300 configured to determine the product of the resistance of testresistor 310 and the capacitance of capacitor 321 (e.g., an RC product).It is noted that test resistor 310, precision capacitor 320, RCoscillator 330, counter 340, bus 341, control lines 342 and referenceclock 350 correspond, respectively, to test resistor 210, precisioncapacitor 220, RC oscillator 230, counter 240, buss 241, control lines242 and reference clock 250 as discussed with respect to FIG. 2 above,and each corresponding element may be configured to exhibit the samefeatures and/or operate substantially the same as its counterpart. Inaddition, calibration system 300 includes capacitor 321 and switch 360,where switch 360 may be used to isolate capacitor 321 from the rest ofcalibration system 300. As explained more fully below, waveform 331 maybe generated when switch 360 is open, and waveform 332 may be generatedwhen switch 360 is closed.

Capacitor 321 may be an exemplary capacitor or capacitor networkconfigured to facilitate calibration of similarly fabricated capacitorsand RC circuits on the same die. For example, capacitor 321 may have apre-determined capacitance configured to be within a particular range ofother capacitors on the same die in order to simulate structuralsimilarity, or may be configured to produce a waveform 332, whenconnected to test resistor 310 and precision capacitor 320, with arelatively long period in order to provide a higher precisioncalibration. Capacitor 321 may comprise one or more metal capacitors,for example, or may be any other type of capacitor that can befabricated on a semiconductor wafer. As is known in the art, the actualcapacitance of a particular metal capacitor may vary from itspre-determined capacitance from wafer to wafer, process-run toprocess-run, and from temperature to temperature, much like aconventional resistor, as explained above.

Switch 360 may be any semiconductor switch that can be formed on asemiconductor wafer and configured to isolate capacitor 321 fromcalibration system 300 according to a control signal provided overcontrol lines 342, such that switch 360 and RC oscillator 330 cangenerate first and second waveforms 331 and 332 with first and secondperiods corresponding to, e.g., substantially dependant upon, theresistance of test resistor 310, the capacitance of precision capacitor320, and, depending on the status of switch 360, the capacitance ofcapacitor 321.

As with RC oscillator 230 above, although RC oscillator 330 is shown inFIG. 3 as including test resistor 310, capacitor 320, switch 360 andcapacitor 321 according to a specific configuration, the particulararrangement is not meant to limit the present inventive concepts. Forexample, although not explicitly shown in FIG. 3, RC oscillator 330 mayconnect to each of test resistor 310, precision capacitor 320 andcapacitor 321 over multiple signal paths in order to facilitate aparticular RC oscillator topology, such as a topology producingsquare-wave waveforms, for example, or a topology producing first andsecond waveforms with highly differentiated periods.

Counter 340, using a technique similar to the one used by counter 240 inFIG. 2 above, can be configured to provide first and second countscorresponding to first and second periods of first and second waveforms331 and 332, as generated by RC oscillator 330 using switch 360, to thedigital portion of the die over bus 341. As will be explained more fullybelow, the first and second counts may be used to determine an RCproduct of test resistor 310 and capacitor 321, thereby calibrating thatproduct for similarly fabricated structures across the semiconductordie. In addition, also explained below, the first and second counts mayalso be used to determine the resistance of test resistor 310 and thecapacitance of capacitor 321, thereby calibrating that type of resistorand that type of capacitor for the entire semiconductor die. Thus, thepresent invention is capable of calibrating resistors, RC products andcapacitors in a single-die semiconductor device with only a minimaladdition of circuitry over that required by the present inventiveconcepts for calibrating resistors alone.

Turning to FIG. 4, FIG. 4 shows flowchart 400 a illustrating a methodfor on-chip calibration of a resistor, an RC product, and a capacitoraccording to an embodiment of the present invention. Certain details andfeatures have been left out of flowchart 400 a that are apparent to aperson of ordinary skill in the art. For example, a step may consist ofone or more substeps or may involve specialized equipment or materials,as known in the art. Steps 410 through 470 indicated in flowchart 400 aare sufficient to describe one embodiment of the present invention;however, other embodiments of the invention may make use of stepsdifferent from those shown in flowchart 400 a. It is noted that FIG. 3illustrates a system capable of performing the method of flowchart 400a, and so steps 410 through 470 are described with reference tocalibration system 300 in FIG. 3.

Referring now to step 410 of the method embodied in FIG. 4, step 410 offlowchart 400 a comprises generating a first waveform from an RCoscillator formed on a semiconductor die. As shown in FIG. 3, firstwaveform 331 may be generated from RC oscillator 330 by using a controlsignal over control lines 342 to open switch 360 and isolate capacitor321 from the rest of the circuit. A signal on control lines 342 may begenerated by a digital portion of a semiconductor die, for example, whena calibration is desired, such as when a temperature change is detected,or periodically throughout operation of the semiconductor device.

Continuing with step 420 in FIG. 4, step 420 of flowchart 400 acomprises using a counter and a reference clock to measure a firstperiod of the first waveform generated in step 410. As explained abovewith reference to FIG. 3, counter 340 may measure a first period offirst waveform 331 by counting a number of cycles of reference clock 350between, for example, some number of signal edges or zero crossings offirst waveform 331. Counter 340 may then forward the count to thedigital portion of the semiconductor device for further processing. Asnoted above, counter 340 may begin measuring a first period wheninitialized by control lines 342, for example, such as when acalibration is desired. As is known in the art, the precision of themeasure of the first period of first waveform 331 can be increased byincreasing the frequency of reference clock 350 and/or by increasing thenumber of signal edges or zero crossings of first waveform 331 sensed bycounter 340 before completing its count, for example. The total numberof signal edges or zero crossings for a particular count may becontrolled, for example, through use of control signals over controllines 342.

Referring now to step 430 in FIG. 4, step 430 of flowchart 400 acomprises determining a resistance of an exemplary resistor in the RCoscillator using the first period of the first waveform and apre-determined capacitance of a precision capacitor. As is known in theart, the period of an RC oscillator may be mathematically dependent onthe resistance of a constituent resistor (e.g., test resistor 310)multiplied by the capacitance of a constituent capacitor (e.g.,precision capacitor 320). As a result, the resistance of test resistor310 may be determined with relatively high precision using the firstperiod of first waveform 331, as provided by counter 340 in step 420,and the pre-determined capacitance of precision capacitor 320. Once theresistance of test resistor 310 is known, all similarly fabricatedresistors residing on the same semiconductor wafer may be calibratedaccordingly. Thus, the present invention can provide an entirely on-chipresistor calibration for a semiconductor device, allowing conventionalfabrication techniques to be used in high precision applications.

Moving now to step 440 in FIG. 4, step 440 of flowchart 400 a comprisesgenerating a second waveform from the RC oscillator of steps 410 through430 by switching an exemplary capacitor into the RC oscillator circuit.As shown in FIG. 3, second waveform 332 may be generated from RCoscillator 330 by using control lines 342 and switch 360 to connectcapacitor 321 into the circuit. As explained above with reference tostep 410, a signal on control lines 342 may be generated by a digitalportion of a semiconductor device as part of a calibration process whena calibration is desired.

Next, step 450 in FIG. 4 comprises using the counter and reference clockof step 420 to measure a second period of the second waveform generatedin step 440. Similar to step 420 described above, counter 340 maymeasure and then forward the measure of the second period to the digitalportion of the semiconductor device for further processing.

Continuing with step 460 in FIG. 4, step 460 of flowchart 400 acomprises determining an RC product of the exemplary resistor andexemplary capacitor using the first and second periods of the first andsecond waveforms. As explained above, the period of an RC oscillator maybe dependent on the product of the resistance of a constituent resistorand the capacitance of a constituent capacitor (e.g., the RC product).When switch 360 in FIG. 3 is closed and capacitor 321 is connected toprecision capacitor 320 and test resistor 310, as shown in FIG. 3, theresistance of the circuit is the resistance of test resistor 310, butthe capacitance of the circuit is the capacitance of precision capacitor320 added to the capacitance of capacitor 321, as is known in the art.Consequently, the second period of the second waveform is dependent onthe resistance of test resistor 310 multiplied by the sum of thecapacitances of precision capacitor 320 and capacitor 321. As a result,the RC product of test resistor 310 and capacitor 321 can be determinedwith relatively high precision by subtracting the second period from thefirst period. Once the RC product of the test resistor 310 and capacitor321 is known, all similarly fabricated RC circuits on the samesemiconductor device may be calibrated accordingly. Thus, the presentinvention can provide an entirely on-chip RC product calibration for asemiconductor device, allowing conventional fabrication techniques to beused in high precision applications. Furthermore, the present inventioncan do so with only minimal additional circuitry over that required bythe present inventive concepts to calibrate resistors on the samedevice.

Finally, step 470 in flowchart 400 a comprises determining a capacitanceof the exemplary capacitor using the RC product and the resistance ofthe exemplary resistor. Once the RC product of test resistor 310 andcapacitor 321 has been determined, such as in step 460, for example, thecapacitance of capacitor 321 can be calculated with relatively highprecision using the actual resistance of test resistor 310 as provided,for example, in step 430. As before, once the capacitance of capacitor321 is known, then all similarly fabricated capacitors residing on thesame semiconductor device may be calibrated accordingly. Thus, thepresent invention can provide an entirely on-chip capacitor calibrationfor a semiconductor device, allowing conventional fabrication techniquesto be used in high precision applications. Furthermore, the presentinvention can do so with only minimal additional circuitry over thatrequired to calibrate resistors on the same device, and with noadditional circuitry over that required to calibrate an RC product forRC circuits on the same device.

Thus, because the present system and method can provide a resistorcalibration without the need for an external connection, the cost andcomplexity of resistor calibration is significantly reduced as comparedto conventional techniques. Furthermore, because the present method doesnot require an iterative process, a resistor calibration may bedetermined in a shorter time and using less power than conventionalmethods, which allows the calibration to be performed more often,thereby providing a more precise calibration over, for example, varyingtemperatures. As such, semiconductor devices utilizing the presentinventive concepts may leverage conventional and inexpensive fabricationtechniques to implement technology requiring higher precision and lesspower than can be provided by conventional means.

From the above description of the invention it is manifest that varioustechniques can be used for implementing the concepts of the presentinvention without departing from its scope. Moreover, while theinvention has been described with specific reference to certainembodiments, a person of ordinary skill in the art would appreciate thatchanges can be made in form and detail without departing from the spiritand the scope of the invention. Thus, the described embodiments are tobe considered in all respects as illustrative and not restrictive. Itshould also be understood that the invention is not limited to theparticular embodiments described herein but is capable of manyrearrangements, modifications, and substitutions without departing fromthe scope of the invention.

The invention claimed is:
 1. An on-chip calibration system comprising: aresistor-capacitor (RC) oscillator on a semiconductor die, said RCoscillator including a test resistor and a capacitor; a counterfabricated on said semiconductor die, said counter configured to receivean output provided by said RC oscillator as a first input; said on-chipcalibration system configured to determine a resistance of said testresistor using said first input to said counter.
 2. The on-chipcalibration system of claim 1, wherein said output of said RC oscillatorcomprises a period substantially proportional to a product of saidresistance and a pre-determined capacitance of said capacitor.
 3. Theon-chip calibration system of claim 2, wherein said counter isconfigured to use a reference clock to measure a first period of a firstwaveform provided by said RC oscillator as said output, said firstperiod being combined with said pre-determined capacitance to determinesaid resistance.
 4. The on-chip calibration system of claim 3, furthercomprising another capacitor coupled to said RC oscillator by a switch.5. The on-chip calibration system of claim 4, wherein said RC oscillatorprovides a second waveform to said counter while said another capacitoris connected to said RC oscillator.
 6. The on-chip calibration system ofclaim 5, wherein said counter is configured to use said reference clockto measure a second period of said second waveform, said second periodbeing combined with said first period to determine an RC product of saidtest resistor and said another capacitor.
 7. The on-chip calibrationsystem of claim 1, wherein said capacitor comprises ametal-insulator-semiconductor (MIS) capacitor.
 8. The on-chipcalibration system of claim 1, wherein said capacitor comprises ametal-insulator-semiconductor (MIS) varactor.
 9. The on-chip calibrationsystem of claim 1, wherein said capacitor comprises ametal-oxide-semiconductor (MOS) varactor.
 10. The on-chip calibrationsystem of claim 1, wherein said test resistor comprises a polysiliconresistor.
 11. The on-chip calibration system of claim 1, furthercomprising another capacitor coupled to said RC oscillator by a switch.12. The on-chip calibration system of claim 11, wherein said anothercapacitor comprises a metal capacitor.
 13. The on-chip calibrationsystem of claim 11, wherein said system is configured to determine an RCproduct of said test resistor and said another capacitor.
 14. Theon-chip calibration system of claim 13, wherein said RC product iscombined with said resistance to determine a capacitance of said anothercapacitor.
 15. A method comprising: generating an output by aresistor-capacitor (RC) oscillator on a semiconductor die, said outputcorresponding to a test resistor and a capacitor of said RC oscillator;receiving said output as a first input by a counter fabricated on saidsemiconductor die; determining a resistance of said test resistor usingsaid first input.
 16. The method of claim 15, wherein said output ofsaid RC oscillator comprises a period substantially proportional to aproduct of said resistance and a pre-determined capacitance of saidcapacitor.
 17. The method of claim 15, wherein said capacitor comprisesa metal-insulator-semiconductor (MIS) capacitor.
 18. The method of claim15, wherein capacitor comprises a metal-insulator-semiconductor (MIS)varactor.
 19. The method of claim 15, further comprising: couplinganother capacitor into said RC oscillator by a switch; determining an RCproduct of said test resistor and said another capacitor.
 20. The methodof claim 19, further comprising using said RC product and saidresistance to determine a capacitance of said another capacitor.
 21. Asystem comprising: a resistor-capacitor (RC) oscillator on asemiconductor die, said RC oscillator including a resistor and acapacitor; circuitry fabricated on said semiconductor die, saidcircuitry configured to receive an output provided by said RC oscillatoras a first input; said system configured to determine a resistance ofsaid resistor using said first input to said circuitry.